Field of the Invention
The present invention relates to an image forming apparatus such as a copier machine or a laser beam printer.
Description of the Related Art
Density correction control is performed in image forming apparatuses. For example, US Patent Application Publication No. 2003-0049039 discloses an image forming apparatus that forms a density correction image in a non-image region during an image forming operation, and determines image forming conditions for adjusting the image density, based on a result of measuring the density correction image with a sensor.
Also, in an electrophotographic image forming apparatus, a change in the capacitance of the photosensitive member brings about a change in the output image. It is known that the capacitance of the photosensitive member changes, for example, when the film thickness of a charge transfer layer of the photosensitive member decreases. The charging characteristics (sensitivity) of the photosensitive member change due to changes in the capacitance of the photosensitive member. Accordingly, the amount of developer that adheres to the photosensitive member changes.
The image forming apparatus executes maximum density control that determines the image forming conditions regarding the maximum density and executes gradation control in which control is performed such that the density of each gradation achieves a target density. In the case where maximum density control is executed, the image forming apparatus forms a measurement image on the photosensitive member and controls the image forming conditions for adjusting the maximum density based on the result of measuring the measurement image with a measuring unit. Here, when maximum density control is performed, a measurement image is formed that corresponds to a predetermined input signal value that is lower than the maximum input signal value, rather than forming a measurement image that corresponds to the maximum input signal value. However, when the capacitance of the photosensitive member changes due to, for example, changes in the film thickness of the photosensitive member, there is a possibility that the image forming conditions cannot be controlled to a high degree of accuracy, even if maximum density control is executed.